ReasoningBlock: a steps variant with per-step rows and a duration summary #85

Workbench's thread collapses tool work into one "Worked through N steps · Xs" row that expands to per-step rows (read / ran / saved glyph, tool name, summary, duration). ReasoningBlock today renders only text inside a details element, so Workbench keeps a local component. A steps variant with a duration on the summary would let it adopt react-ui.